1. Field of the Invention
The present invention relates to a hydraulic joint structure including two members which are screw-engaged with each other, with an annular seal member interposed therebetween, in order to mutually connect hydraulic passages formed in the members.
2. Description of the Related Art
Japanese Patent No. 2576998 discloses a hydraulic joint structure of the above-described type. In the disclosed hydraulic joint structure, two members to be screw-engaged together have respective pressure-contact surfaces which oppose each other and prevent loosening between thread portions of the two members. When the two members are screw-engaged together, the pressure-contact surfaces of the members come into pressure contact with each other to thereby form a space on the downstream side (external space side) of a seal member. In the case of a hydraulic joint structure having the above-described configuration, seal inspection is performed in order to guarantee seal performance. Specifically, in a state in which a gap of about 0.5 mm is formed between the pressure-contact surfaces of the two members, pressurized working fluid is applied to the upstream side of the seal member, and the external space is visually inspected so as to determine whether the working fluid leaks to the external space via the gap. In the case where the seal inspection is performed in a state in which the two members have been tightly screw-engaged together in order to eliminate the gap between the pressure-contact surfaces, even when the seal member is defective, the working fluid does not leak to the external space, by virtue of the seal action of the pressure-contact surfaces, thereby rendering the visual inspection unreliable. Notably, the seal performance of the pressure-contact surfaces is influenced by variations in the environment, such as temperature variation and permanent set of the materials of the members (i.e., the seal action is unstable), and therefore is not expected to continue for a long term.
After completion of the above-described seal inspection, in order to eliminate the gap between the pressure-contact surfaces, a process for tightly screw-engaging the two member each other must be performed, thereby deteriorating work efficiency. Further, in order to enable seal inspection to be performed in a state in which the two members have been tightly screw-engaged together to thereby eliminate the gap between the pressure-contact surfaces, a communication groove may be formed on one of the pressure-contact surfaces in order to enable working fluid that has leaked because of a seal defect to flow to the external space via the communication groove. However, when the communication groove extends in a radial direction of the members, the distance between the external space and the seal member is short, and foreign matter or water is likely to enter and reach the seal member via the communication groove, possibly damaging the seal member.